1. Field of the Invention
This invention broadly relates to a drive mechanism for timed reciprocation of a double sickle assembly for use with harvesting and mowing equipment. More particularly, the invention concerns a drive mechanism having dual toothed belts (sometimes called "cog" belts) which are twisted to efficiently transfer rotary motion from a drive shaft to two sprockets oriented transversely to the drive shaft and eccentrically coupled to sway bars that are, in turn, connected to the sickles for oscillation of the latter. The center line of the driven sprocket connected to the sway bar is carefully aligned with the pitch circle of the belt that is trained about a sprocket affixed to the drive shaft to avoid imposition of undue wear on either of the sprockets or the belt.
2. Description of the Prior Art
Relatively large mowers and harvesters are often provided with two reciprocating sickles that extend across opposite sides of the front of the machine. Typically, each sickle reciprocates in a longitudinal direction by means of a respective sway bar that is carried along the sides of the machine and is coupled to an outermost end of the corresponding sickle. In turn, both of the sway bars are oscillated in some fashion or another by a drive mechanism which receives power from a common, rotating drive shaft.
As an example, U.S. Pat. No. 4,246,742 dated Jan. 27, 1981 describes and illustrates a drive mechanism for sway bars of a double sickle assembly wherein two connecting rods coupled to ends of the sway bars remote from the sickles are connected to eccentric cranks affixed to a central drive shaft. Each of the sway bars ocillates about a vertical pivot axis located in the middle of each sway bar, and ball and socket assemblies are used for drivingly interconnecting the forward end of each sway bar and the corresponding sickle to enable free, non-binding reciprocating motion of the latter.
The connecting rods of double sickle mechanisms of the type described in U.S. Pat. No. 4,246,742 are coupled to opposite sides of the crank on the central drive shaft so that the sway bars oscillate in a timed fashion and in opposite directions to enable the sickles connected thereto to simultaneously reciprocate in opposite directions and in a synchronous manner. As a result, vibrational forces which tend to be established by one of the sickles moving in one direction are counteracted by the forces generated by the other sickle moving in the opposite direction, such that the resultant sum of the vibrational forces is significantly diminished.
However, sway bars that are pivotal about a central axis located between a connecting rod coupled to the drive shaft and one end of a sickle bar are normally relatively long and thereby are of a sizable mass. Such construction necessarily increases the overall cost of the drive mechanism and requires the use of relatively large, expensive bearings for coupling the sway bars to the frame of the machine. Sway bars of this type occupy a substantial amount of space on each side of the machine.
Another type of drive mechanism which may be used in a double sickle assembly when chain-driven is shown in U.S. Pat. No. 3,941,003, dated Mar. 2, 1976. In U.S. Pat. No. 3,941,003, a relatively short sway bar is pivotally connected on one end to the frame of the machine and is connected at the opposite end to one end of a sickle; in addition, linkage is connected to the sway bar adjacent the sickle and is centrifugally coupled to a rotatable shaft extending transversely to the plane of reciprocation of the sway bar in order to impart movement to the latter and thereby the sickle.
The sickle drive mechanism shown in U.S. Pat. No. 3,941,003 includes a right angle gear box that is connected to the rotatable shaft and driven by a pulley that receives an endless V-belt which, in turn, is driven by one of two pulleys connected to a central drive shaft. This type of construction avoids the use of relatively large sway bars, although sizable expense and maintenance costs are associated with right angle gear boxes. More importantly, the use of smooth V-belts and pulleys effectively precludes the likelihood that each reciprocating sickle will inevitably move in synchronous fashion and in an opposite direction to the direction of movement of the other sickle.
In the past, belts having teeth have been used in other applications where the belt is intended to transmit rotary motion from one shaft to another, especially where it is desired to ensure movement of the shafts in timed, synchronous fashion. The teeth of the belt, whether of an elongated, semi-cylindrical toothed-type configuration or of a trapezoid shape, are serially received in a series of complementally configured grooves formed in the sprockets so that, for all practical purposes, slippage between the belt and either sprocket is precluded and timing between both sprockets cannot be lost.
However, it has long been believed that toothed belts, or belts with semi-cylindrical teeth, must not experience any degree of twist in the belt about its longitudinal axis as the belt moves along its closed loop path of travel and about the sprockets. To this end, much effort is normally undertaken to ensure that the centers of all sprockets receiving the belt lie in a common plane. It has been thought in this regard that any degree of twist experienced by the belt will cause the teeth to experience undue wear during engagement with grooves on the sprockets and considerably shorten the life of the belt. As a consequence, toothed belts have heretofore not been utilized to translate rotary motion about a first axis into rotary motion about a second axis which is inclined relative to the first axis in applications such as would be desirable in harvesting headers in order to avoid the need for right angle gear boxes and the like.